I. Field
The present invention relates generally to communication, and more specifically to techniques for multiplexing multiple data steams in a wireless multi-carrier communication system.
II. Background
A multi-carrier communication system utilizes multiple carriers for data transmission. These multiple carriers may be provided by orthogonal frequency division multiplexing (OFDM), some other multi-carrier modulation techniques, or some other construct. OFDM effectively partitions the overall system bandwidth into multiple (N) orthogonal frequency subbands. These subbands are also referred to as tones, carriers, subcarriers, bins, and frequency channels. With OFDM, each subband is associated with a respective subcarrier that may be modulated with data.
A base station in a multi-carrier communication system may simultaneously transmit multiple data streams. Each data stream may be processed (e.g., coded and modulated) separately at the base station and may thus be recovered (e.g., demodulated and decoded) independently by a wireless device. The multiple data streams may have fixed or variables data rates and may use the same or different coding and modulation schemes.
Multiplexing multiple data streams for simultaneous transmission may be challenging if these streams are variable in nature (e.g., have data rates and/or coding and modulation schemes that change over time). In one simple multiplexing scheme, the multiple data streams are allocated different time slots or symbol periods using time division multiplexing (TDM). For this TDM scheme, only one data stream is sent at any given moment, and this data stream uses all subbands available for data transmission. This TDM scheme has certain undesirable characteristics. First, the amount of data that may be sent in the smallest time unit allocable to a given data stream, which may be viewed as the “granularity” for the data stream, is dependent on the coding and modulation scheme used for the data stream. Different coding and modulation schemes may then be associated with different granularities, which may complicate the allocation of resources to the data streams and may result in inefficient resource utilization. Second, if the granularity for a given coding and modulation scheme is too large relative to the decoding capability of a wireless device, then a large input buffer may be required at the wireless device to store received symbols.
There is therefore a need in the art for techniques to efficiently multiplex multiple data streams in a multi-carrier communication system.